AC motor with reactor interposed between AC motor and power source

ABSTRACT

A reactor ( 32 ) and a switch ( 35 ) are interposed in parallel between U-phase, V-phase and W-phase on a power source side ( 31 ) and U, V and W terminals on a motor side ( 33 ). A changeover switch ) 37 ) is interposed between Z, X and Y terminals on the motor side ( 33 ) and the U, V and W terminals on the motor side ( 33 ). When the switch ( 35 ) is set to OFF, the changeover switch ( 37 ) is set to ON, and the switch ( 35 ) is set up so as to interconnect Z, X and Y terminals, windings of the motor are set up in the form of Y-connection, so that the motor and a power source are connected directly to each other. On the other hand, when the changeover switch ( 37 ) is switched over to OFF, and the switch ( 35 ) is set up so as to interconnect Z, X and Y terminals to the U, V and W terminals, the windings of the motor are set up in the form of Δ-connection, so that the motor and the power source are connected together through the reactor ( 32 ).

TECHNICAL FIELD

This invention relates to a three-phase AC motor with a reactorinterposed between the AC motor and a power source side for the purposeof suppressing generation of heat in a rotor and a stator by decreasinga higher harmonic component included in voltage.

BACKGROUND ART

In an AC motor which employs a three-phase alternating current drivesource, in some cases, the drive of such an AC motor is controlled bysupplying voltage of non-sinusoidal waveform such as stepped waveform tothe motor. Such a voltage of non-sinusoidal waveform contains a higherharmonic component. A loss resulting from the higher harmonic componentin the supply voltage ultimately produces heat, which causes heatoperation in the motor.

In general, the AC motor has both high-speed output characteristics togenerate high output at high-speed revolution and low-speed outputcharacteristics to generate high output at low-speed revolution. Thehigh-speed output characteristics or the low-speed outputcharacteristics are attained by varying the number of turns of primarywinding in the motor or by selecting between Y-connection andΔ-connection.

Heat generated due to the higher harmonic component contained in drivevoltage of the motor presents a problem particularly when the motor isoperated with the connection for high-speed output characteristics.Thus, in order to suppress the generation of heat due to the higherharmonic components as described above, a reactor is interposed betweenthe power source and the motor to attenuate the higher harmoniccomponent contained in the drive voltage. The reactor is effective insuppressing the generation of heat in a rotor and a stator of the motorat high-speed revolution, whereas impedance of the reactor causes adecrease in the amount of current supplied to the primary winding atlow-speed revolution, resulting in reduction of output.

With reference to FIGS. 8A and 9B, description will first be given of amethod for attaining two kinds of characteristics, that is,characteristics for high-speed operation and those for low-speedoperation, by switching over primary winding connection in an AC motor,which employs a three-phase alternating drive source.

Referring to FIG. 8A, primary winding comprises U-phase winding 1,V-phase winding 2 and W-phase winding 3 of a motor, which are set up inthe form of a Y-connection, and this Y-connection is adapted to attainthe characteristics for low-speed operation. The U-phase winding 1 has Uand X terminals, the V-phase winding 2 has V and Y terminals, and theW-phase winding 3 has W and Z terminals. The X, Y and Z terminals of thewindings are interconnected. Then, U, V and W terminals on a powersource side 31 are respectively connected to the U, V and W terminals ofthe windings 1, 2 and 3 set up in the form of the Y-connection.

FIG. 8B shows Δ-connection switched over from the connection(Y-connection) of the windings shown in FIG. 8A. This Δ-connection isadapted to attain the characteristics for high-speed operation. In FIG.8B, the U, V and W terminals are respectively connected to the Z, X andY terminals. Then, the U, V and W terminals on the power source side 31are respectively connected to the U, V and W terminals of the windings1, 2 and 3 in Δ-connection.

Next, referring to FIGS. 9A and 9B, a description will now be given of amethod for attaining two kinds of characteristics, that is,characteristics for high-speed operation and those for low-speedoperation, by switching over a voltage application terminal of a primarywinding in an AC motor, which employs a three-phase alternating drivesource.

Referring to FIG. 9A, first and second U-phase windings 10, 11 connectedin series, first and second V-phase windings 12, 13 connected in seriesand first and second W-phase windings 14, 15 connected in series are inY-connection. Then, a terminal U1 of the first U-phase winding, aterminal V1 of the first V-phase winding and a terminal W1 of the firstW-phase winding are respectively connected to U, V and W terminals on apower source side 31. Thus, the number of turns in each phase comes tothe sum of turns of two windings (10, 11; 12, 13; 14, 15). Thisconnection is suitable for attaining the characteristics for low-speedoperation.

Referring to FIG. 9B, a terminal U2 of the second U-phase winding, aterminal V2 of the second V-phase winding and a terminal W2 of thesecond W-phase winding in the windings in Y-connection shown in FIG. 9Aare respectively connected to the U, V and W terminals on the powersource side 31. Thus, the number of turns in each phase becomes equal tothe number of turns of a single winding (11, 13, 15), so that the numberof turns in each phase is less than in the case shown in FIG. 9A, and asa result, this connection is suited for obtaining the characteristicsfor high-speed operation.

Next, referring to FIGS. 10A and 10B, a description will now be given ofa prior art, in which a reactor is interposed between a power source anda motor in switching between Y-connection and Δ-connection shown inFIGS. 8A and 8B.

Referring to FIG. 10A, a reactor 32 is interposed between U, V and Wterminals on a power source side 31 and U, V and W terminals of a motor33. A first switch 35 is interposed between the reactor 32 and the U, Vand W terminals of the motor 33. Further, a second switch 36 isconnected to Z, X and Y terminals of the motor 33.

In FIG. 10A, since the first switch 35 is at an off or open or closedposition and the second switch 36 is at on position, the U, V and Wterminals on the power source side 31 are respectively connected to theU, V and W terminals of the motor 33 through the reactor 32, and the X,Y and Z terminals of the motor are interconnected, so that Y-connectionis formed. That is, a wiring shown in FIG. 10A is similar to that shownin FIG. 8A, except that the reactor 32 is interposed between the U, Vand W terminals on the power source side 31 and the U, V and W terminalsof the motor 33.

Referring to FIG. 10B, the first switch 35 in FIG. 10A is switched overto a closed or on-position, and the second switch 36 in FIG. 10A isswitched over to an open or off-position. As a result, the U, V and Wterminals on the power source side 31 are respectively connected to Uand Z, V and X and W and Y terminals of the motor 33 through the reactor32, so that Δ-connection is set up. That is, a wiring shown in FIG. 10Bis similar to that shown in FIG. 8B, except that the reactor 32 isinterposed between the U, V and W terminals on the power source side 31and the U, V and W terminals of the motor 33.

In the foregoing, as shown in FIGS. 10A and 10B, the reactor 32 isinterposed between the power source side 31 and the motor 33 in both thecases where switching to Y-connection (FIG. 10A) is made for attainingthe characteristics for low-speed operation and where switching to theΔ-connection (FIG. 10B) is made for attaining the characteristics forhigh-speed operation. Thus, when the characteristics for high-speedoperation are attained by the Δ-connection, this reactor 32 is effectivein suppressing the generation of heat by decreasing the higher harmoniccomponent. On the other hand, when an attempt to attain thecharacteristics for low-speed operation is made through switching toY-connection, the reactor functions so as to reduce output.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide an improvedthree-phase AC motor with a reactor interposed between this AC motor anda power source side for the purpose of suppressing generation of heat ina rotor and a stator by decreasing a higher harmonic component includein voltage, wherein the reactor is inhibited from causing the fall ofoutput when winding connection is switched over to attain thecharacteristics for low-speed operation, or when a voltage applicationterminal of a winding is switched over.

In order to attain the above object, a motor as a mode according to thepresent invention comprises a connection switching means for switchingprimary winding connection in a three-phase AC motor betweenY-connection and Δ-connection; a reactor interposed between a powersource and the motor; and a reactor interposition changeover means,connected to the reactor, for selective switching between the state, inwhich voltage is supplied from the power source to the motor sidethrough the reactor, and the state, in which voltage is supplied fromthe power source to the motor side without passing through the reactor.

In a motor as another mode according to the present invention, a primarywinding in the motor is provided with a voltage application terminalgroup to increase the number of turns in the primary winding, and asecond voltage application terminal group to decrease the number ofturns in the primary winding. A reactor is interposed between a powersource and the motor. A reactor interposition changeover means isconnected to the reactor for selective switching between the state wherevoltage is supplied from the power source to the motor side through thereactor, and the state where voltage is supplied from the power sourceto the motor side without passing through the reactor.

According to the present invention, the reactor is disconnected when theprimary winding in the motor is set up in the form of joint orconnection for low-speed operation, while the reactor is connected whenthe primary winding in the motor is set up in the form of joint orconnection for high-speed operation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a wiring diagram of connection between a power source sideand a motor side as a first embodiment according to the presentinvention, in which a switch and a changeover switch are set to thestate for low-speed operation;

FIG. 1B is a wiring diagram of connection as the first embodimentaccording to the present invention, in which the switch and thechangeover switch shown in FIG. 1A are switched over to the state forhigh-speed operation;

FIG. 2A is a wiring diagram of connection between a power source sideand a motor side as a second embodiment according to the presentinvention, in which first and second switches are set for low-speedoperation;

FIG. 2B is a wiring diagram of connection as the second embodimentaccording to the present invention, in which the first and secondswitches shown in FIG. 2A are switched over to the state for high-speedoperation;

FIG. 3A is a wiring diagram of connection between a power source sideand a motor side as a third embodiment according to the presentinvention, in which a switch and a changeover switch are set forlow-speed operation;

FIG. 3B is a wiring diagram of connection as the third embodimentaccording to the present invention, wherein the switch and thechangeover switch shown in FIG. 3A are switched over for high-speedoperation;

FIG. 4A is a wiring diagram of connection between a power source sideand a motor side as a fourth embodiment according to the presentinvention, in which first and second switches are set for low-speedoperation;

FIG. 4B is a wiring diagram of connection as the fourth embodimentaccording to the present invention, wherein the first and secondswitches shown in FIG. 4A are switched over to the state for high-speedoperation;

FIG. 5 is a view for explaining a wiring of connection between the powersource side and the motor side shown in FIG. 1B;

FIG. 6 is a view for explaining a wiring of connection between the powersource side and the motor side shown in FIG. 2B;

FIG. 7 is a wiring of connection between the power source side and themotor side shown in FIGS. 3B and 4B;

FIG. 8A is view showing the state, in which primary winding in athree-phase motor is set up in the form of Y-connection;

FIG. 8B is a view showing the state, in which primary winding in athree-phase motor is set up in the form of Δ-connection;

FIG. 9A is a view showing the state, in which primary winding in athree-phase motor is provided with a voltage application terminal groupto increase the number of turns and a voltage application terminal groupto decrease the number of turns, and a power source is connected to thevoltage application terminal group to increase the number of turns;

FIG. 9B is a view showing the state, in which a power source isconnected to the voltage application terminal group to decrease thenumber of turns shown in FIG. 9A;

FIG. 10A is a wiring diagram of a prior art including a reactorinterposed between a power source side and a motor side, and first andsecond switches connected to the motor side, wherein the first andsecond switches are switched over so that primary winding in a motor isset up in the form of Y-connection; and

FIG. 10B is a wiring diagram showing the state, in which the first andsecond switches shown in FIG. 10A are switched over so that primarywinding in a motor is in Δ-connection.

BEST MODE OF EMBODYING THE INVENTION

A description will first be given of embodiments, as first and secondembodiments, in which a reactor is interposed between a power sourceside and a motor side when the characteristics for high-speed operationare required, while the reactor is disconnected when the characteristicsfor low-speed operation are required, where primary winding connectionin an AC motor employing a three-phase alternating drive source isswitched over to a Y-connection so as to attain the characteristics forlow-speed operation, while primary winding connection described above isswitched over to a Δ-connection so as to attain the characteristics forhigh-speed operation.

First Embodiment

A description will now be given below of a first embodiment withreference to FIGS. 1A and 1B.

Referring to FIG. 1A, a power source side 31 includes a three-phasepower source having U-phase, V-phase and W-phase, and a motor side 33 isprovided with U terminal, V terminal, W terminal, Z terminal, X terminaland Y terminal. A reactor 32 and a switch 35 are interposed in parallelbetween the U-phase, V-phase and W-phase on the power source side 31 andthe U terminal, V terminal and W terminal on the motor side 33. Further,a changeover switch 37 is interposed between the Z terminal, X terminaland Y terminal on the motor side 33 and the U terminal, V terminal and Wterminal on the motor side 33.

In FIG. 1A, since the switch 35 is turned on, current on the powersource side 31 tends to flow toward the motor side 33 through both theswitch 35 and the reactor 32. However, since the reactor 32 exerts ahigh impedance, the current on the power source side 31 is supplied tothe motor side 33 mostly through the switch 35. That is, the reactor 32in FIG. 1A is kept in a substantially disconnected state. On the otherhand, the changeover switch 37 is switched over so as to interconnectthe Z terminal, X terminal and Y terminal on the motor side 33. Thus, inFIG. 1A, the primary winding in the motor is set up in the form ofY-connection suitable for attaining the characteristics for low-speedoperation, and besides, the reactor 32 is substantially in the state ofdisconnection from the power source side 31 and the motor side 33. Thatis, the power source side 31 and the motor side 33 in FIG. 1A areconnected to each other as shown in FIG. 8A.

Referring to FIG. 1B, the switch 35 in FIG. 1A is switched over to theoff-position, and the changeover switch 37 is switched over so as toconnect the Z terminal, X terminal and Y terminal on the motor side 33to the U terminal, V terminal and W terminal on the motor side 33. As aresult, the motor side 33 is brought into the Δ-connection suitable forattaining the characteristics for high-speed operation, and besides,current on the power source side 31 is made to be supplied to the motorside 33 through the reactor 32. That is, the power source side 31 andthe motor side 33 in FIG. 1B are connected to each other as shown inFIG. 5. Incidentally, reference character R in FIG. 5 denotes a reactorin each phase.

As described above, the switch 35 in FIGS. 1A and 1B has a function ofmaking the reactor 32 to be interposed between the power source side 31and the motor side 33 or to be disconnected from the power source sideand the motor side by selecting between off state and on state of theswitch. Further, the changeover switch 37 functions as a connectionswitching means capable of switching the primary winding connection inthe motor between the Y-connection and the Δ-connection.

Second Embodiment

A description will now be given of a second embodiment with reference toFIGS. 1A and 2B.

Referring to FIG. 2A, the U-phase, V-phase and W-phase on the powersource side 31 are directly connected to the U terminal, V terminal andW terminal on the motor side 33. Further, the U-phase, V-phase andW-phase on the power source side 31 are respectively connected to the Zterminal, X terminal and Y terminal on the motor side 33 through serialconnectors composed of the first switch 35 and the reactor 32. Further,a second switch 36 is connected to the Z terminal, X terminal and Yterminal on the motor side 33.

In FIG. 2A, the first switch 35 is turned off, and the second switch 36is turned on. Therefore, the Z terminal, X terminal and Y terminal onthe motor side 33 are interconnected without being connected to theU-phase, V-phase and W-phase on the power source side 31, therebyproviding a Δ-connection suitable for attaining the characteristics forlow-speed operation. Besides, the reactor 32 is disconnected from thepower source side 31 and the motor side 33. As a result, the powersource side 31 and the motor side 33 in FIG. 2A are connected togetheras shown in FIG. 8A.

Referring to FIG. 2B, the first switch 35 in FIG. 2A is switched over toON, while the second switch 36 in FIG. 2A is switched over to OFF. As aresult, the Z terminal, X terminal and Y terminal on the motor side 33are respectively connected to the U terminal, V terminal and W terminalon the motor side 33 through the reactor 32, thereby providing theΔ-connection suitable for attaining the characteristics for high-speedoperation. As a result, the power source side 31 and the motor side 33in FIG. 2B are connected together as shown in FIG. 6. Incidentally,reference character R in FIG. 6 denotes a reactor in each phase.

As described above, the first switch 35 in FIGS. 2A and 2B has afunction for interposing the reactor 32 between the power source side 31and the motor side 33 or disconnecting the reactor from the power sourceside and the motor side by selecting between ON state and OFF state ofthe first switch. Further, the second switch 36 functions as aconnection switching means capable of switching primary windingconnection in the motor between the Y-connection and the Δ-connection.

A description will now be given of the third and fourth embodiments, inwhich the reactor is interposed between the power source side and themotor when the characteristics for high-speed operation are required,while the reactor is disconnected when the characteristics for low-speedoperation are required, in a case where a voltage application terminalof the primary winding of the motor is switched over to vary the numberof turns so as to attain the characteristics for low-speed operation orthose for high-speed operation.

The third and fourth embodiments are applied to the primary winding ofthe motor, in which the first and second U-phase windings 10, 11connected in series, first and second V-phase windings 12, 13 connectedin series, and first and second W-phase windings 14, 15 connected inseries are set up in the form of Y-connection as shown in FIGS. 9A and9B. Then, the first and second U-phase windings 10, 11 are respectivelyprovided with terminals U1, U2, the first and second V-phase windings12, 13 are respectively provided with terminals V1, V2, and the firstand second W-phase windings are respectively provided with terminals W1and W2.

Third Embodiment

A description will now be given of the third embodiment with referenceto FIGS. 3A and 3B.

Referring to FIG. 3A, the U-phase, V-phase and W-phase on the powersource side 31 are connected to a changeover switch 37 through aparallel connector composed of the reactor 32 and the switch 35.Further, this changeover switch 37 is selectively switched over to thestate, in which connection to the terminals U1, V1 and W1 on the motorside 33 is made and the state, in which connection to the terminals U2,V2 and W2 is made.

In FIG. 3A, the switch 35 is set to OFF, and the changeover switch 37 isswitched over to the side of the terminals U1, V1 and W1 on the motorside 33. As a result, the U-phase, V-phase and W-phase on the powersource side 31 are connected to the terminals U1, V1 and W1 on the motorside 33 through the reactor 32 and simultaneously through the switch 35.Thus, since the terminals U1, V1 and W1 on the motor side 33 areconnected to the terminals U1, V1 and W1 on the motor side 33, thenumber of turns of the winding in each phase of the motor comes to thesum of the turns of the first and second windings (windings 10 and 11,12 and 13, and 14 and 15 in FIG. 9A), so that the state suitable forattaining the characteristics for low-speed operation is achieved.Furthermore, even if the power source side 1 is connected through theparallel connectors composed of the switch 35 and the reactor 32, thecurrent on the power source side 31 is supplied to the motor side 33mostly through the first switch 35, since the reactor 32 exerts highimpedance. As the result, the reactor 32 in FIG. 3A is placed in thesubstantially disconnected state. Thus, the power source side 31 and themotor side 33 in FIG. 3A are connected to each other as shown in FIG.9A.

In the case of FIG. 3B, the switch 35 in FIG. 3A is switched over toOFF, and the changeover switch 37 in FIG. 3A is switched over to theside of the terminals U2, V2 and W2 on the motor side 33. As a result,the U-phase, V-phase and W-phase on the power source side 31 arerespectively connected to the terminals U2, V2 and W2 on the motor side33 through the reactor 32. Since the U-phase, V-phase and W-phase on thepower source side 31 are respectively connected to the terminals U2, V2and W2 on the motor side 33, the number of turns of the winding in eachphase of the motor becomes equal to the number of turns of correspondingone of the second windings (the winding 11, 13, 15 in FIG. 9A), thusproviding the number of turns suitable for attaining the characteristicsfor high-speed operation, and further, the reactor 32 is interposedbetween the windings 11, 13, 15 and the power source side 31. Thus, thepower source side 31 and the motor side 33 in FIG. 3B are connected toeach other as shown in FIG. 7.

As described above, the switch 35 in FIGS. 3A and 3B has a function ofinterposing the reactor 32 between the power source side 31 and themotor side 33 and disconnecting the reactor from the power source sideand the motor side by selecting between ON state and OFF state of theswitch 35. Further, the changeover switch 37 has a function ofincreasing and decreasing the number of turns of the windings in theprimary winding of the motor.

Fourth Embodiment

A description will now be given of a fourth embodiment with reference toFIGS. 4A and 4B.

Referring to FIG. 4A, the U-phase, V-phase and W-phase on the powersource side 31 are respectively connected to the terminals U2, V2 and W2on the motor side 33 through serial connectors composed of the firstswitch 35 and the reactor 32. Further, the U-phase, V-phase and W-phaseon the power source side 31 are respectively connected to the terminalsU1, V1 and W1 on the motor side 33 through the second switch 36.

In FIG. 4A, the first switch 35 is set to OFF, and the second switch 36is set to ON. Thus, the U-phase, V-phase and W-phase on the power sourceside 31 are connected to the terminals U1, V1 and W1 on the motor side33 without interposing the reactor 32. That is, the power source side 31and the motor side 33 are connected to each other as shown in FIG. 9A,and the number of turns in the primary winding of the motor is increasedto provide the connection suitable for attaining the characteristics forlow-speed operation.

In the case of FIG. 4B, the first switch 35 in FIG. 4A is switched overto ON, and the second switch 36 is switched over to OFF. As a result,the U-phase, V-phase and W-phase of the power source side 31 areconnected to the terminals U2, V2 and W2 on the motor side 33 throughthe reactor 32. As a result, the power source side 31 and the motor side33 are connected to each other as shown in FIG. 7, and the number ofturns in the primary winding of the motor is decreased to provide theconnection suitable for attaining the characteristics for low-speedoperation.

What is claimed is:
 1. An AC motor with a reactor interposed between apower source and the motor, comprising: a connection switching means forswitching primary winding connection in a three-phase AC motor betweenY-connection and Δ-connection, a reactor interposed between the powersource and the motor; and a reactor interposition changeover meansconnected to said reactor for selectively switching between the state,in which voltage is supplied from the power source to the motor sidethrough said reactor, and the state, in which the voltage is suppliedfrom the power source to the motor side without passing through saidreactor, wherein said reactor employed in connection with the switchingof the winding between the Y-connection and the Δ-connection suppressesincreases of harmonies due to inductance changes caused by switchingbetween the Y-connection and the Δ-connection.
 2. An AC motor with areactor interposed between a power source and the motor, comprising: aconnection changeover switch for switching primary winding connection ina three-phase AC motor between Y-connection and Δ-connection; and areactor and a switch respectively interposed in parallel between a powersource of said motor and said changeover switch; wherein said reactor isinterposed between the power source and the motor in a manner such thatthe reactor can be connected thereto and disconcerted therefrom byon-off operation of said changeover switch, wherein said reactoremployed in connection with the switching of the winding between theY-connection and the Δ-connection suppresses increases of harmonies dueto inductance changes caused by switching between the Y-connection andthe Δ-connection.
 3. An AC motor with a reactor interposed between apower source and the motor, comprising: a connection changeover switchfor switching primary winding connection in a three-phase AC motorbetween Y-connection and Δ-connection; and serial connectors composed ofa switch and a reactor and interposed between first, second and thirdterminals of the three-phase AC motor and fourth, fifth and sixthterminals of the three-phase AC motor; wherein the power source isconnected to the motor through said reactor or directly withoutinterposing said reactor by on-off operation of said changeover switch,and said reactor employed in connection with the switching of thewinding between the Y-connection and the Δ-connection suppressesincreases of harmonies due to inductance changes caused by switchingbetween the Y-connection and the Δ-connection.
 4. An AC motor with areactor interposed between a power source and the motor, comprising: aprimary winding provided for the motor and having a voltage applicationterminal group for increasing the number of turns in said primarywinding and another voltage application terminal group for decreasingthe number of turns in said primary winding; a reactor interposedbetween a power source and the motor; and a reactor interpositionchangeover means connected to said reactor for selectively switchingbetween the state, in which voltage is supplied from the power source tothe motor side through said reactor, and the state, in which the voltageis supplied from the power source to the motor side without passingthrough said reactor; wherein said reactor employed in connection withswitching between the voltage application and the another voltageapplication suppresses increases of harmonies due to inductance changescaused by switching between voltage applications.
 5. An AC motor with areactor interposed between a power source and the motor, comprising: achangeover switch for selecting either a connection to a voltageapplication terminal group to increase the number of turns in a primarywinding of a three-phase AC motor or a connection to a voltageapplication terminal group to decrease the number of turns in saidprimary winding; and a switch and a reactor interposed in parallelbetween said changeover switch and a power source; wherein the powersource is connected to the voltage application terminal group toincrease the number of turns in the primary winding without interposingthe reactor or the power source is connected to the voltage applicationterminal group to decrease the number of turns in the primary windingthrough the reactor by on-off operation of said changeover switch, andsaid reactor employed in conjunction with switching between connectionssuppresses increases of harmonies due to inductance changes caused byswitching connections.
 6. An AC motor with a reactor interposed betweena power source and the motor, comprising: a first switch interposedbetween the power source and a voltage application terminal group todecrease the number of turns in a primary winding of a three-phase ACmotor; and serial connectors composed of a second switch and saidreactor and interposed between the power source and a voltageapplication terminal group to increase the number of turns in saidprimary winding; wherein when said first switch is set to ON and saidsecond switch set to OFF, the power source is connected directly to thevoltage application terminal group to increase the number of turns inthe primary winding, while when said firs switch is switched over to OFFand sad second switch is switched over to ON, the power source isdirectly connected to the voltage application terminal group to decreasethe number of turns in the primary winding through the reactor, and saidreactor employed in connection with switching between said first andsecond switches suppresses increases in harmonics due to inductancechanges caused by changing switches.